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首页> 外文期刊>The Journal of Chemical Physics >Origin of methyl torsional barrier in 1-methyl-2-(1H)-pyridone
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Origin of methyl torsional barrier in 1-methyl-2-(1H)-pyridone

机译：1-甲基-2-（1H）-吡啶酮中甲基扭转屏障的起源

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摘要

The laser induced fluorescence excitation and single vibronic excitation dispersed fluorescence spectra have been studied for supersonic jet cooled l-methyl-2(lh)-pyridone.The methyl torsional bands and some low frequency vibrational transitions were assigned for both ground and excited states.The torsional parameters V_3=244 cm~(-1) and V_6=15cm~(-1) for the ground state and V_3=164 cm~(-1) and V_6=40 cm~(-1) for the excited state were obtained.To get the insight into the methyl torsional barrier,ab initio calculations were performed and compared with the experimental results.Origin of potential barrier was traced by partitioning the barrier energy into changes in bond-antibond interaction,structural,and steric energies accompanying methyl rotation using natural bond orbital analysis.The role of local interactions in ascertaining the barrier potential reveals that its nature cannot be understood without considering the molecular flexing.The hyperconjugation between CHsigma and ring pi observed in lowest unoccupied molecular orbital (LUMO) stabilizes the methyl group conformer that undergoes a 60deg rotation in the excited state with respect to that of the ground state,and it is the change in LUMO that plays important role in the excited state barrier formation.
机译：研究了超声喷射冷却的1-甲基-2（lh）-吡啶酮的激光诱导荧光激发和单振动激发分散的荧光光谱，并分别为基态和激发态分配了甲基扭转带和一些低频振动跃迁。获得了用于基态的扭转参数V_3 = 244 cm〜（-1）和V_6 = 15cm〜（-1）以及用于激发态的V_3 = 164 cm〜（-1）和V_6 = 40 cm〜（-1）为了深入了解甲基扭转屏障，进行了从头算起的计算并将其与实验结果进行比较。通过将屏障能划分为伴随甲基旋转的键-反键相互作用，结构能和空间能的变化来追踪势垒的起源使用自然键轨道分析。局部相互作用在确定势垒势中的作用表明，如果不考虑分子弯曲，就无法理解其本质.CHsigma与pi环之间的超共轭在最低未占据分子轨道（LUMO）中观察到的分子稳定了在受激态下相对于基态旋转60度的甲基构象体，而LUMO的变化在受激态势垒形成中起着重要作用。

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